Atrial fibrillation (AF) is a disorder found in millions of Americans. A heart in normal sinus rhythm receives an electrical signal from which it develops the well coordinated heart beat. AF occurs when something imparts a change to the electrical signal received by the heart resulting in, for example, uncontrolled and uncoordinated beating of the atria. While typically not fatal, the uncoordinated heart beat associated with AF results in blood pooling and clotting which, in turn, can lead to stroke. Approximately 15 percent of strokes occur in people with AF.
Various ablation systems, including catheters and surgical tools, are commonly used to ablate cardiac tissue to treat atrial fibrillation. The ablation system may incorporate an ablating portion which is placed upon the posterior wall of the left atrium, for example, where one or more lesions are then created as part of a desired lesion set or pattern.
With the move to less invasive procedures, a need has developed for catheters and surgical ablating tools which provide the user, typically an electrophysiologist or cardiac surgeon respectively, more precision and control, along with increased freedom of motion with respect to the controlled guidance of the ablating portions. Problems of guidance and control of ablation devices within the heart are further exasperated when preformed as a minimally invasive ablation procedure on a beating heart. Moreover, the varying anatomic differences from one patient to another lead to greater challenges involving the steering and positioning of the ablating portion of an ablation system within the left atrium.
With these general problems in mind, ablation systems have been designed which generally focus typically on one specific procedural requirement. For example, some ablation systems provide for an ablating portion mounted on and forming the distal tip of a steerable ablation catheter, the catheter being more easily guided and directed by a user to a target tissue site where tissue is to be ablated. However, even with these systems users find it difficult to reach certain areas of the left atrium, such as the intersection of tissue near the right superior pulmonary vein ostium and septal wall. Additionally, procedures performed with such systems are more time consuming since only a single small point lesion is created at any given time.
Other catheter systems are designed to create long linear lesions. While creating longer lesions allowing for faster procedure times when compared to point ablating systems, such linear ablating systems present additional challenges. Still other ablation systems are directed to isolating the pulmonary veins from the remaining atrial tissue. One such group of devices are designed to ablate a circumferential tissue region about a pulmonary vein ostium. Another group of circumferential ablation devices are designed to create circumferential tissue lesions along the inner wall of the pulmonary vein itself. While all such ablation systems provide a corresponding specialized advantage, they are generally problematic and present different challenges for the end user, as discussed in more detail immediately below.
Most catheter ablation systems require complex motions, for example movements in at least two planes, to move the ablating device from one ablation site to the next, in order to create the desired continuing lesion. Currently, most ablation procedures in the left atrium, for example, employ systems with tip electrodes which are mounted upon and form the distal tip end of the ablation catheter system. The user, typically an electrophysiologist, then guides the tip to a point of interest on the posterior wall of the left atrium and performs the point ablation procedure. Once a first point ablation is created, the user then guides the tip electrode to a subsequent point along the posterior wall and creates an additional point ablation, typically in communication with the first. This process continues until the desired lesion pattern is created through the interconnecting of numerous point ablations to create the desired lesion pattern, isolating the pulmonary veins from the remaining atrial tissue for example. These systems are sometimes referred to as “drag and burn” systems since they require the user to drag the tip electrode to a desired location and burn, or otherwise ablate, the target tissue at that location.
There are other limitations to point ablation systems. For example, while applying the necessary translational force to the tip portion to ensure proper contact with the target tissue for purposes of ablation, if the distal shaft portion of the ablating device is not substantially normal to the target tissue surface, the distal tip will slip, or otherwise move across the target tissue. This positioning or placement problem is exasperated during beating heart procedures where the user must predict and work in unison with cardiac movement when placing the ablating portion upon the target tissue surface. Another factor leading to placement problems is the fact that the endocardial surface of the left atrium posterior wall, apart from the location adjacent to the pulmonary vein ostia, can be quite smooth.
In practice, users of point ablation systems typically use costly support equipment to provide historic and current position information of the ablating portion with respect to anatomical cardiac structures and previously created lesions. The support equipment, while useful, is extremely costly and requires additional personnel to operate, ultimately increasing procedure costs.
Other drag and burn systems require numerous accessories and more complex methods which require additional time to complete the desired lesion set as part of the ablation procedure. See for example, U.S. Pat. No. 5,814,028 which discloses a system comprising numerous guide sheaths and ablation catheters designed, when specifically paired, to create numerous very specific ablation lines, or tracks, in the left and right atriums to treat atrial fibrillation. Aside from the inherent problems with point ablation devices, these relatively complex devices and methods require additional procedure time which can lead to user fatigue, and ultimately an unsafe working environment, as well as increasing procedure costs.
Still another problem with point ablation devices having ablating tip portions is the risk of perforation. As the device is advanced to engage the atrial tissue, translational force is applied by the user to ensure proper contact with the target tissue. Since the translational force is directed to the target tissue at a point, great care must be taken to ensure that excessive force is not used which may result in perforation of the atrial wall. Excessive force, coupled with the application of ablative energy, may increase the risk of atrio-esophogeal fistula, especially for radiofrequency point ablating systems. See, for example, “Atrio-Esophageal Fistula as a Complication of Percutaneous Transcatheter Ablation of Atrial Fibrillation”, Carlo Pappone, MD, PhD, et al., Circulation, Jun. 8, 2004 which discusses two cases where the left atrium was perforated with radio frequency based point ablation systems.
Creating continuous curvilinear lesions with linear ablating devices, while in theory providing an ability to create certain lesion patterns more quickly, is also problematic. Creating continuous lesions with curvilinear ablating devices requires the user to create a first lesion and then reposition the ablating portion adjacent to one end of the previously created linear lesion to create a second lesion, the second lesion being continuous with the first. With linear ablating devices, especially radio frequency based devices which, in theory, can create a more thin lesion line, due to viewing limitations during the procedure it is often very difficult to properly position the linear ablating portion in order to create the successive continuous linear lesions as part of a desired lesion pattern. Also, as with the point ablation procedures described above, typically support equipment is needed to ensure that the proper placement has been achieved.
See for example U.S. Pat. Nos. 5,582,609 and 6,544,262 which disclose various loop and spline structures used to create linear lesions. Such systems, however, in additional to the general problems stated above, require complex movements to ensure proper placement of the ablating portions of the devices for creation of continuous lesions, especially in a beating heart procedure. Often the user is required to move the ablating portion in multiple planes, deflections along two or more planes for example, in order to properly place the ablating portion. Moreover, the user may need to rotate the ablating catheter to further orient the ablating portion upon the target tissue and adjacent a previously created lesion in order to create a second lesion continuous with the first. Such complex movements make it very difficult to determine whether successive ablations are continuous without the use of additional procedural support equipment or other accessories.
Another problem with most linear ablating systems is they require a user to manipulate the elongated ablating portion to a point parallel to and adjacent target tissue. Such linear ablating systems become very dependent on the approach to the target tissue itself. This, in turn, limits the ability of the ablation system to create a multitude of lesions as part of a desired lesion pattern. This is often the case when the procedure is theoretically complete, however the patient is not in normal sinus rhythm. The user must then figure out where to create additional lesions in order to clinically complete the procedure. Such a decision should not be limited or dictated by the design of the ablation system itself. Rather, the ablation system should be able to create the desired lesion irregardless of its location or orientation within the heart.
See for example U.S. Pat. No. 6,106,522 which discloses linear ablating devices used to apply energy in a straight or curvilinear position in contact with tissue to form elongated lesion patterns. Such devices are problematic since they put heavy burdens on delivery systems, requiring such systems to steer the ablating portions to a point parallel to and adjacent target tissue. Creating the broad range of lesions necessary for the treatment of atrial fibrillation is very difficult with such systems, requiring a freedom of motion that is unavailable in the current offerings. Also, see U.S. Pat. No. 5,680,860 which teaches the creation of linear lesions through activation of certain radio frequency electrodes along the linear lesion line of interest, as part of a larger spiral embodiment. Such devices, however, are large in size and hard to properly place to ensure proper contact is made by and between the ablating portion and the target tissue, allowing the creation of the linear lesion. As is discussed in more detail below with respect to other spiral devices, such systems do not have ablating portions which apply sufficient contact force along the entire length of the ablating portion.
Moreover, such linear ablating devices as described above, due to the nature of their design, typically do not possess the necessary flexibility to be able to hold or retain the ablating portion adjacent to a target tissue while maintaining proper tissue contact, a necessity for radio frequency based ablation devices.
Additionally, linear ablating systems do not build on the procedural strengths electrophysiologists have acquired and further developed over the course of time performing a great number of ablation procedures utilizing steerable ablating systems with point ablation tip portions. Rather than approaching the target tissue from a direction more normal to the target tissue surface, many linear ablating systems require the user to learn new skills to perfect the associated ablation procedures.
As part of a desired lesion pattern, some electrophysiologists use the point ablating devices described above to create lesions around the pulmonary veins, isolating one pulmonary vein from the left atrial tissue for example. Such isolating procedures require precise placement of the ablating portion near a pulmonary vein ostium. While some areas in the left atrium, for example, are more readily accessible, other areas, such as near the junction between the septal wall and the ostium of the right superior pulmonary vein, are not as easily accessible. Placement of the ablating portion near a right pulmonary vein ostium via a transseptal approach is especially challenging since such placement requires sharp catheter bends near the transseptal opening along the septal wall. As with point ablating procedures described above, many times the user simply relies on costly lab equipment to try to guide him to a desired target tissue location.
Others have simply tried to encircle a pulmonary vein and simultaneously ablate a circumferential region of tissue surrounding the vein. See for example U.S. Pat. Nos. 6,024,740, 6,164,283 and 6,955,173 which disclose expandable balloon based ablating structures designed to simultaneously or instantaneously create circumferential ablations around a pulmonary vein ostium. These expandable balloon based ablation devices typically include anchoring devices, or other protruding devices or structures, which are used for anchoring or guiding the device to the ostium of the pulmonary vein. These structures prevent the use of such devices for creation of associated linear lesions as part of a desired lesion pattern. Such expandable balloon structures also substantially block the blood flowing through the pulmonary vein and into the left atrium, the true consequences of which are not completely understood.
Such circumferential ablating devices also generally do not provide consistent circumferential contact between the ablating portion and the circumferential tissue surrounding the ostium, such contact being required for creation of a corresponding circumferential lesion. This is more noticeable in radio frequency ablation systems or thermal conductive ablation systems, such as cryogenic or resistive heating ablation systems for example, which require direct tissue contact for ablative current to flow or sufficient thermal conduction to occur, respectively, for tissue ablation. For example, balloon structures for cryogenic ablating systems are typically fixed in overall dimension and do not posses the flexibility needed to properly engage a circumferential region of tissue surrounding an ostium of a pulmonary vein, the specific anatomic shape which can vary dramatically from patient to patient.
Radiofrequency ablating devices which rely on a continuous elastic or superelastic metallic structure, such as nitinol for example, for both placement and ablation are particularly susceptible to contact issues since these materials, despite their name, do not have the requisite flexibility to engage a continuous tissue surface in order to create a continuous lesion therein. While thermal conduction may complete lesions associated with some of these problematic non-contact areas, not all may be resolved. Nor is there a simple way to discover where the discontinuity lies since the exact degree of contact between the ablating portion and the target tissue, along the length of the ablating portion, is not readily known.
See also U.S. Pat. Nos. 6,572,612, 6,960,206 and 6,923,808 which disclose loop devices designed to engage a circumferential region of tissue surrounding a pulmonary vein ostium, immediately and simultaneously ablating the circumferential region. As with the balloon structures discussed above, while the immediate devices possess the flexibility to longitudinally pass through a guiding catheter and then take on a circumferential shape once within the left atrium, they are not flexible enough to be able to adequately engage the non-linear circumferential region of tissue consistent with the creation of a continuous lesion thereupon.
Most of such spiral ablation systems are also flawed due to their inability to apply requisite constant contact pressure between the length of the spiral structures and the corresponding circumferential region of tissue. Rather, as the user applies axial force, the force is only applied to the most proximal section of the ablating portion, the most distal section not necessarily making the preferred tissue contact for formation of a corresponding continuous lesion.
More recently, ablating devices have been developed to help address the tissue contact problem associated with ablating circumferential regions of tissue around a pulmonary vein ostium. See for example, U.S. Pub. Nos. US20040106920 and US20050267453 which disclose systems which laterally ablate tissue at a given radial position near a pulmonary vein ostium. However, such systems are problematic since they rely on a generally consistent tissue surface along the radial path about the pulmonary vein ostium. As the system is radially rotated in order to create the desired circumferential lesion, at some point the ablating device may no longer be engaging the target tissue due to the specific anatomic structure of the patient. To resolve this issue, it may be needed to advance the ablating portion toward the pulmonary vein in order to laterally engage target tissue adjacent to the pulmonary vein ostium. However, such advancement, considering this lateral ablating approach, may jeopardize the continuity of the currently created lesion with previously created lesions.
Some ablation devices have been developed to ablate the inner wall of the pulmonary vein itself, at a point within the pulmonary vein. For example, U.S. Pat. No. 6,503,247 and U.S. Pub. No. US20050267463 disclose systems for ablating the inner wall of the pulmonary vein to isolate undesirable signals originating in the pulmonary veins from the remainder of the left atrial tissue. Such systems are undesirable since ablation of the inner wall of the pulmonary vein can lead to stenosis which, in turn, can then lead to serious respiratory problems including shortness of breath or dysnpea, severe coughing or hemoptysis, chest pain and pneumonia. See, for example, “Clinical Presentation, Investigation, and Management of Pulmonary Vein Stenosis Complicating Ablation for Atrial Fibrillation,” Douglas L. Packer, M.D., et al., Circulation, Feb. 8, 2005 which discusses such problems.
More recently, various ablation systems have been developed which allow for the creation of larger area ablations for the treatment of ventricular tachycardia. See U.S. Pat. Nos. 5,582,609, and 6,699,241 for exemplary systems used to create large volumetric lesions for the treatment of ventricular tachycardia. Neither address creating continuous lesions with area ablations for the treatment of atrial fibrillation, as in the present application.